In the block or head of an internal combustion engine, lubrication is provided typically via a single primary longitudinal bore supplying oil to a plurality of intersecting secondary bores leading to individual camshaft bearings and hydraulic lash adjusters (HLAs) or hydraulic lifters (HLs).
Typical switchable cam followers for varying the lift and/or timing of combustion valves of an engine, whether in an engine head or engine block, utilize hydraulically actuated lock pins to implement a mode change in the system. For example, a switchable valve lifter used in a cam-in-block engine functions as a conventional hydraulic valve lifter when low oil pressure is supplied to a switching gallery; when high oil pressure is enabled, a lock pin is displaced and the lifter switches to a deactivated mode of operation wherein camshaft motion is lost in the lifter and not transmitted to the associated combustion valve stem.
In a similar way, a switchable rocker arm assembly, as used in a cam-in-head changes between a high lift and a low lift mode of operation (known in the art as a two-step roller finger follower (RFF)) or between a high lift and a no lift mode of operation (known in the art as a deactivating RFF) depending upon the oil pressure in the switching gallery. A typical prior art switchable rocker arm assembly includes an articulated switchable RFF disposed between an engine camshaft lobe and a valve stem. The switchable RFF includes a hydraulically-actuated lock pin to engage or disengage the articulated members. Typically, the lock pin is engaged between the articulated members by a return spring. The lock pin is disengaged by application of high pressure hydraulic fluid, typically engine oil provided by the engine's oil distribution system, to overcome the return spring. The switchable RFF is pivoted on an HLA at an end opposite to the valve-engaging end. The HLA is mounted in a residence bore in the engine head. The HLA is supplied with engine oil from a molded or bored single channel oil gallery in the engine head to feed the lash adjuster mechanism therein, and oil also flows from the HLA to the switchable RFF through a central opening in the ball head of the HLA and a mating passage in the switchable RFF. When oil is supplied through the single channel oil gallery at low pressure, the lock pin spring overcomes the oil pressure and the switchable RFF is in the latched mode. To overcome the lock pin spring, the oil pressure is increased through the HLA via an oil control valve (OCV) to a higher pressure sufficient to cause the lock pin to be retracted, placing the switchable RFF in its unlatched mode. The single channel oil gallery thus doubles as a switching gallery to the switchable RFF and an oil supply gallery for lubricating the camshaft bearings.
A problem arises in using a single channel oil gallery in such a dual mode, for either a cam-in-block switchable lifter or a cam-in-head switchable RFF, in that the pressure logic of a switchable application mandates that oil pressure in the gallery be reduced when latching of the device is desired while, at the same time, having to sufficiently lubricate the camshaft bearings. Under these conditions, the reduced oil pressure can result in premature bearing wear or outright failure.
One known approach to preventing this problem is to provide a secondary switching gallery adjacent the primary gallery specifically for supplying the switchable RFF (or switchable lifter) so as to dedicate the primary oil gallery for only the lash adjustment and camshaft bearing lubrication requirements. Disadvantageously, this approach requires significant changes in the prior art oil circuitry to provide independent oil feeds for the switching functions. See, for example, U.S. Pat. No. 6,557,518, wherein the switching function for a switchable RFF is resident in the HLA itself. Such a design most conveniently requires an entirely new two-piece plunger arrangement and reduces significantly the volume of the HLA low-pressure chamber, raising concerns for potential noise upon cold start of the engine. Further, it can be difficult and expensive to provide two adjacent galleries so close together within an engine block or head; and further, significant leakage can occur between the two galleries along the wall of the HLA residence bore.
What is needed in the art is an oil gallery circuit wherein the camshaft bearings are lubricated via a first oil gallery which does not communicate with the switchable cam follower and the latching/unlatching functions of the switchable cam follower are satisfied from a second, independently controlled oil gallery, and wherein both galleries are provided within a single, preferably prior art, longitudinal bore in the engine block or head.
What is further needed in the art is a means for segregating the second oil gallery from the primary oil gallery to permit use of a plurality of OCVs for synchronized mode changes of the switchable cam followers, without requiring extensive modification of a conventional engine block or cylinder head.
What is further needed in the art is a means for segmenting the second oil gallery for selectively and separately controlling switchable cam followers within a single bank of cylinders.
It is a principal object of the present invention to meet simultaneously the camshaft oil supply requirements and the oil supply requirements of the switchable cam followers of an internal combustion engine without requiring significant changes in prior art engine block or head configurations.